The objective of the proposed research is to investigate the learning abilities of the fetus in utero. Although concern for the healthy development of the fetus continues to spawn considerable interest in prenatal behavior, relatively little is yet known about how a fetus behaves and responds to changes within its uterine environment. In spite of technological advances, methodological problems and ethical considerations have limited the study of the human fetus to indirect monitoring and postnatal inference. Therefore, direct observation and experimentation is possible only with nonhuman subjects. Techniques developed in our laboratory and elsewhere now enable precise manipulation of the intrauterine environment of rat fetuses and observation of fetal behavior in utero. In brief, these procedures involve exposing the rat fetus in utero to a taste/odor stimulus followed by either an aversive intraperitoneal injection of LiCl or a reinforcing intraoral infusion of milk. After the pregnant female is prepared by chemomyelotomy, which produces an irreversible spinal anesthesia without the use of drugs, fetuses that have been conditioned using aversive or appetitive procedures can be delivered out of the uterus into a warm saline bath, maintaining the placental-uterine attachment intact, and their behavior observed. Fetuses that have been conditioned using aversive or appetitive procedures can be reexposed to the taste-odor stimulus and their responses analyzed to evaluate a variety of hypotheses concerning fetal learning in utero. Four general studies of fetal learning are proposed: (1) to determine the earliest prenatal age at which learned taste/odor aversions can be acquired; (2) to characterize fetal responses in utero to aversively conditioned taste/odor stimuli as a function of developmental age; (3) to evaluate the ability of fetuses to acquire and express appetitive learning in utero; and (4) to investigate the influence of behavioral state (e.g., fetal activation) and environmental context (e.g., ambient temperature) on the acquisition and expression of fetal learning in utero. These experiments will provide needed information on the behavior of the fetus in aversive and appetitive learning situations and begin to explore the role of fetal learning in subsequent behavioral development.